The present invention relates to a vehicle headlamp having a so-called projector type lamp unit.
Heretofore, there is a known vehicle headlamp so arranged as to allow switching of low and high beams by moving a shade. For example, JP-A-2000-207918 discloses a vehicle headlamp having a beam switching mechanism of such a shade driving type.
The beam switching mechanism of the shade driving type has been applied to a so-called parabolic lamp unit in the vehicle headlamp mentioned in the above Japanese Patent Publication. However, the beam switching mechanism of the shade driving type is also applicable to the projector type lamp unit.
Nevertheless, in the case of the projector type lamp unit, because the image of a light source for forming a luminous distribution pattern becomes larger than what is produced in the parabolic lamp unit due to its structure, in case where switching of beams is carried out by the shade driving, there develops a problem of making it infeasible to sufficiently increase luminous intensity in a hot zone (high luminous intensity area) at the time of high-beam emission.
The aforesaid problem will be explained in detail as follows:
FIGS. 15A and 15B show luminous distribution patterns formed by beam emission from a projector type lamp unit to which a beam switching mechanism of a shade driving type is applied: FIG. 15A refers to a low-beam luminous distribution pattern; and FIG. 15B to a high-beam luminous distribution pattern.
In a low-beam luminous distribution pattern P(L)xe2x80x2 of FIG. 15A, the brightness of an area A near a cut-off line CL on the opposite lane side is preferably kept at a predetermined value or lower in view of preventing glare from being given to an oncoming car driver. In a high-beam luminous distribution pattern P(H)xe2x80x2 of FIG. 15B, on the other hand, the area A is preferably made as bright as possible as part of the hot zone (high luminous intensity area)
Thus, conflicting demands of light and shade are placed on the area A in both cases of low and high beams and it is considerably difficult to satisfy such demands only by relying on the presence of a shade in the projector type lamp unit in which the image of the light source grows larger. In this case, the problem is that brightness of the hot zone at the time of high-beam emission will have to be sacrificed to a certain degree in view of assigning priority to preventing glare from being given to an oncoming car driver.
An object of the invention is to provide a vehicle headlamp which has a projector type lamp unit for emitting beams forward with predetermined luminous distribution patterns and is capable of improving the luminous intensity of a hot zone at the time of high-beam emission after due consideration for preventing glare from being given to an oncoming car driver at the time of low-beam emission.
The invention is intended to accomplish the object above by providing two kinds of reflector in the respective predetermined positions.
According to the invention, a vehicle headlamp for use in emitting beams forward with predetermined luminous distribution patterns by using a lamp unit comprising a light source arranged on an optical axis extending in the longitudinal direction of a vehicle, a reflector for reflecting light from the light source forward a little to the optical axis, a projection lens provided in front of the reflector, and a shade which is provided between the projection lens and the reflector and used for shading part of the light reflected from the reflector, wherein
a first auxiliary reflector which is provided between the reflector above the optical axis Ax and the projection lens and used for reflecting direct light from the light source downward,
a second auxiliary reflector which is provided between the reflector under the optical axis and the projection lens and used for reflecting the light reflected from the first auxiliary reflector forward.
The kind of the light source is not limited to a specific one but may be any light source, for example, the discharge light emitting portion of a discharge bulb, the filament of an incandescent bulb such as a halogen bulb.
On condition that the first auxiliary reflector is provided between the reflector above the optical axis Ax and the projection lens and used for reflecting direct light from the light source downward, the configuration and the size, for example, of the reflective surface are not limited to specific arrangement.
On condition that the second auxiliary reflector is provided between the reflector under the optical axis Ax and the projection lens and used for reflecting the light reflected from the first auxiliary reflector forward, the configuration and the size, for example, of the reflective surface are not limited to specific arrangement.
With the arrangement shown above, the vehicle headlamp according to the invention has the projector type lamp unit and the first auxiliary reflector is provided between the reflector above the optical axis Ax and the projection lens and used for reflecting direct light from the light source downward, whereas the second auxiliary reflector is provided between the reflector under the optical axis Ax and the projection lens and used for reflecting the light reflected from the first auxiliary reflector forward, so that the following operation/working effect are attainable.
In the projector type lamp unit, though the direct light directed from the light source forward and obliquely upward is not generally used for forming the luminous distribution pattern, the direct light is reflected downward by the first auxiliary reflector first and then reflected forward by the second auxiliary reflector, whereby as the luminous distribution pattern emitted forward from the lamp unit, the luminous distribution pattern (auxiliary luminous distribution pattern) formed by the light reflected from the second auxiliary reflector can be added to the basic luminous distribution pattern formed by the light reflected from the reflector and passed through the projection lens.
At the time of high-beam emission, the luminous intensity of the hot zone can be improved satisfactorily by adding the auxiliary luminous distribution pattern to the basic luminous distribution pattern and then using the auxiliary luminous distribution pattern for the formation of the hot zone. At the time of low-beam emission, on the other hand, glare can be prevented from being given to an oncoming car driver by using only the basic luminous distribution pattern without adding the auxiliary luminous distribution pattern thereto.
Thus, in the vehicle headlamp that causes the projector type lamp unit to emit beams forward with the predetermined luminous distribution patterns according to the invention, it is possible to attempt to improve the luminous intensity of the hot zone at the time of beam emission while glare is prevented from being given to the oncoming car driver at the time of low-beam emission.
Although the configurations of the first and second auxiliary reflectors are not limited to specific ones as described above, the light reflected from the first auxiliary reflector is readily controllable by the second auxiliary reflector by forming the reflective surface of the first auxiliary reflector into an elliptic spherical surface having a first focal point close to the light source and forming the second auxiliary reflector into a secondary curved surface (i.e., a parabolic, an elliptic or a hyperbolic curved surface) having a focal point close to the second focal point of the reflective surface of the first auxiliary reflector.
With the arrangement above, the shade is movably provided whereby to assume a shade position for shading part of the light reflected from the reflector and an exposure position for releasing the shading of the light and wherein when in the shade position, the shade is used for shading the light directed to the second auxiliary reflector from the first auxiliary reflector, whereas when in the exposure position, the shade is used for releasing the shading of the light directed to the second auxiliary reflector from the first auxiliary reflector. Thus, beam emission is carried out with the basic luminous distribution pattern at the time of low-beam emission, whereas the auxiliary luminous distribution pattern can be added to the basic luminous distribution pattern at the time of high-beam emission without necessitating a new mechanism.
In this case, the provision of a through-hole through which the light directed to the second auxiliary reflector from the first auxiliary reflector is allowed to pass therethrough only when the shade is in the exposure position makes it simply possible to shade the light directed to the second auxiliary reflector from the first auxiliary reflector and to release the shading of the light.
With the arrangement above, the direction of beam emission with the auxiliary luminous distribution pattern can be varied by movably providing the second auxiliary reflector, whereby the beam emission can be controlled in a delicate manner corresponding to the travel condition of the vehicle. At this time, the mode of moving the second auxiliary reflector is not specifically restrictive but may inclusive of, for example, pivoting on the horizontal or vertical axis, or linear reciprocating movement in lateral, vertical and longitudinal directions.
When the second auxiliary reflector is movably provided, the auxiliary luminous distribution pattern can be added to the basic luminous distribution pattern at the time of not only high-beam emission but also low-beam emission by switching the directions of the light reflected from the second auxiliary reflector between the high-beam emission and the low-beam emission without shading the light directed to the second auxiliary reflector from the first auxiliary reflector even at the time of low-beam emission.
With the projector type lamp unit as a lamp unit for special use in low-beam emission, the auxiliary luminous distribution pattern formed by the light reflected from the second auxiliary reflector may be addition to the basic luminous distribution pattern (i.e., low-beam luminous distribution pattern) always or timely.